If this is your first dive, do not try to prove anything. Tell the crew if you are nervous, if your ears are sensitive, or if you have not swum in a while. A good first scuba experience should feel slow enough for you to ask questions.
Discover Scuba Diving is built for that pace. You learn how the gear feels, how to breathe through the regulator, and how to signal underwater before the trip turns into sightseeing. The reef is the reward, not the rush.